This technology required the use of electrodes placed on the brain (the volunteers were already going to receive such implants for a normal medical procedure) and the signal was recorded as single words were spoken to the subject. Using computational models the brain waves were translated into audible sounds which were close enough for the original word to be guessed. With hours of repetition it should be possible to perfect the sound, so a guess is not needed, but the researchers recognize this isn’t very helpful. In real life a conversation cannot be repeated over and over again; the conversion has to work on the first try.

This could be a huge advance for people who have lost the ability to speak due to disease or stroke. If neuroscientists can find where imaginary conversation occur within the brain (where one talks to him or herself), then it may be possible to return to these people the ability to talk. That may still be a ways off, but this is an impressive step towards that end. You can listen to the audio of the original words and the converted brainwaves at the source link.